when we measure the specific activity of any sample using Gamma spectroscopy , we always keep the prepared sample in a locked marnilli beaker for one month or more to let radio nuclides in the sample reach the secular equilibrium , but practically do you think this processes effect on the results? and what is the expected error rate in the measurement if we measure the samples immediately with out equilibrium .
The procedure in which the sample is kept in a tight container for about one month is typically used for the measurement of 226Ra , 1 month being the time needed to obtain secular equilibrium between 222Rn and 226Ra (7 times the half-life of 222Rn , 3.8 d). 222Rn itself is much more rapidly in equilibrium with its gamma-emitting progeny (a few hours). Thus, after 1 month, 214Bi and 214Pb have the same activity as 226Ra.
The sample is often put in powder form; in this stage the small grains are exposed to air and Rn can easily escape, but the fraction that escapes cannot be predicted.
Initially the sample also contains some activity of Rn progeny, that decays in a few hours while it is gradually replaced by the Rn decay.
Thus the variation of the activity of 214Bi and 214Po in the sample, just after it is prepared, is not something simple and is hard to predict.
When putting the sample in the container, care must be taken not to leave any empty space, where Rn and its progeny would accumulate, modifying the homegeneity of the activity distribution. It can also be recommended to mix some charcoal powder (~10%) to the sample as Rn is fixed on charcoal, thus keeping the same geometry as Ra and limiting the constraint of tightness of the container (several polymers like PE are not tight for Rn).
The measurement of Ra with the gamma peaks of Rn progeny is preferred to the direct measurement on the 186 keV peak of 226Ra, because this one interferes with a peak of 235U. If U is absent from the sample, e.g. after chemical separation, this measurement is possible without secular equilibrium.
Specific activity is not affected by equilibrium. I suspect you mean total activity.
It is best to wait for secular equilibrium for total activity. You can calculate the final activity if you can determine the activity of the parent nuclide. If you are using progeny to calculate the parent, you can take several measurements with time to determine the growth rate. Error should be small in a well-known system and sufficient counting time.
The procedure in which the sample is kept in a tight container for about one month is typically used for the measurement of 226Ra , 1 month being the time needed to obtain secular equilibrium between 222Rn and 226Ra (7 times the half-life of 222Rn , 3.8 d). 222Rn itself is much more rapidly in equilibrium with its gamma-emitting progeny (a few hours). Thus, after 1 month, 214Bi and 214Pb have the same activity as 226Ra.
The sample is often put in powder form; in this stage the small grains are exposed to air and Rn can easily escape, but the fraction that escapes cannot be predicted.
Initially the sample also contains some activity of Rn progeny, that decays in a few hours while it is gradually replaced by the Rn decay.
Thus the variation of the activity of 214Bi and 214Po in the sample, just after it is prepared, is not something simple and is hard to predict.
When putting the sample in the container, care must be taken not to leave any empty space, where Rn and its progeny would accumulate, modifying the homegeneity of the activity distribution. It can also be recommended to mix some charcoal powder (~10%) to the sample as Rn is fixed on charcoal, thus keeping the same geometry as Ra and limiting the constraint of tightness of the container (several polymers like PE are not tight for Rn).
The measurement of Ra with the gamma peaks of Rn progeny is preferred to the direct measurement on the 186 keV peak of 226Ra, because this one interferes with a peak of 235U. If U is absent from the sample, e.g. after chemical separation, this measurement is possible without secular equilibrium.
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